The present invention relates to an image processing apparatus for displaying an accumulated image of very faint light emitted from an object and an image of a configuration of the object in an overlay fashion.
In recent field-effect transistors (FETs) having small gate length, carriers (electrons or holes) may be accelerated by a strong electric field to such an extent that the internal recombination of the carriers occurs to cause emission of a photon. Carriers in such a state are called "hot carriers". There are some papers reporting the detection of light emission by the hot carriers, though it is very weak.
It is also known that very faint light is emitted in the process of dielectric breakdown of an oxide film. In recent MOS integrated circuits, a voltage of typically 3 V or 5 V is applied across a gate oxide thin film of several hundreds angstroms in thickness. Therefore, the resultant high electric field across the gate oxide film, which reaches several megavolts/cm, may cause dielectric breakdown of the gate oxide thin film very faint light is emitted in the breakdown process.
To locate a faint light emitting point in the object, it is necessary to obtain a combined image in which an accumulated image of the faint light is displayed over an image of a configuration of the object. To this end, an image processing apparatus as shown in FIG. 2 has conventionally been used. Faint light emitted from a faint light emitting object, which ranges from visible light to infrared light, is imaged on an image intensifier by an optical microscope. The formed image is then converted into a television signal by a television camera. The image data thus obtained is accumulated over a long period of time by an accumulation image memory circuit 1, and the accumulated image data is stored therein. The object is externally illuminated to gather image data of the object configuration, and the resultant image data is stored into a configuration image memory circuit 2. The accumulation image data and the configuration image data are superposed on each other by an image superposing circuit, 3, and the superposed image is displayed in an overlay fashion by a display device 4.
Thus, in the conventional image processing apparatus, the faint light image and the configuration image are stored in separate memory circuits in advance at different times, and thereafter the two images are superposed on each other. Therefore, it is impossible to observe a light emitting process of the faint light and a light emitting location in the object in real time. Further, it takes much time to obtain the superposed image.